JPH10197515A - Estimating method of working temperature of cobalt group heat resistant alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a working temperature of Co group heat resistant alloys with high accuracy by using a correlation curve related to a Larson-Miller parameter(LMP) value. SOLUTION: Heating materials of plural Co group heat resistant allays ECY 768 are heated at about 750 to 1000 deg.C for about 5000 hours at the longest in the atmosphere, and secondary carbide is observed on the respective heating materials by a scanning electron microscope, and a change in the average area is quantitatively determined by an image processor. The average area of this secondary carbide shows an excellent correlation with an LMP value being a function of a temperature and time, and the LMP value corresponding to the average area of the secondary carbide is read from this correlation curve, and a metal temperature can be estimated from it and known operation time. Here, the LMP value can be expressed by (273+T)×(C+log t) by using a heating temperature T deg.C, heating working time (t) and a time constant C. A working temperature of the heat resistant alloys ECY 768 can be accurately estimated by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a temperature (also called a metal temperature) during the use of a high-temperature member, particularly a Co-based heat-resistant alloy material used for a long time as a gas turbine stationary blade material.

[0002]

2. Description of the Related Art Conventionally, alloys for which temperature estimation is performed include Ni-based alloys used for gas turbine rotor blades and the like, and low alloy steels used for boiler tubes and the like. With the use of these alloys for a long time at high temperature, structural changes such as coarsening of the γ 'phase or a decrease in the amount of pearlite are observed, and the temperature during use is estimated based on these changes over time. I have.

[0003] Therefore, it is expected that the use temperature of an actual machine member can be estimated if such a temporal change in the microstructure can be confirmed even with a Co-based heat-resistant alloy. This Co
As an example of the base heat-resistant alloy, there is ECY768 (trade name) which is an alloy having a chemical composition shown in the following table.

[0004]

[Table 1]

[0005] Regarding ECY768, a metallographic photograph of ECY768 previously heated in a laboratory at a high temperature for a long time and an ECY768 which has been used for a long time in a real machine have been used.
By comparing the microstructure photographs of No. 768, it was only possible to check the presence or absence of abnormal high temperature use from the precipitation of secondary carbides and the state of coarsening.

[0006]

However, the above-mentioned conventional temperature estimation method uses the ECY7 which has been used at a high temperature for a long time.
Since the metallographic photograph of No. 68 is compared with a reference structural photograph prepared in advance by aging treatment at various temperatures and times, not only is it easy to perform a subjective evaluation, but the temperature range of estimation is wide. There was a drawback that would be a thing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for objectively, quantitatively and accurately estimating a temperature during use of a Co-based heat-resistant alloy which is an actual machine member.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned object, and the gist of the present invention is to provide a method for estimating the use temperature of a Co-based heat-resistant alloy. An object of the present invention is to estimate a service temperature of a Co-based heat-resistant alloy based on a correlation curve associated with a Larson-Miller parameter which is a numerical value quantitatively representing the accompanying structural change. The Co-based heat-resistant alloy to which the present invention can be applied contains carbon or chromium on which carbides are precipitated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for estimating the use temperature of a Co-based heat-resistant alloy according to the present invention will be described below with reference to the drawings. The optical microstructure of the Co-based heat-resistant alloy ECY768 is
As shown in FIG. 1, MC type primary carbide 1, M ₂₃ C ₆ type primary carbide 2, M ₂₃ C ₆ type secondary carbide 3 at the boundary of dendrite, M ₂₃ C ₆ type secondary carbide 4 at the center of dendrite and matrix Of the five types. Dendrite is a collection of crystals having a dendritic outer shape, which is observed in the solidification structure of molten metal. For M ₂₃ C ₆ type secondary carbides 4 of these dendrites center portion, or coarse due to a high temperature for a long time heating, or by increasing exhibit significant tissue changes.

Focusing on the coarsening and increasing of the carbide, the correlation between the average area of the entire structure and the Larson-Miller parameter value (hereinafter referred to as the LMP value) is obtained, and the correlation is obtained. LM corresponding to the average area of secondary carbide in the metallographic structure of the member used in actual equipment from the obtained correlation curve
The P value is read and the temperature is estimated from the value and the known operation time. Here, the LMP value is obtained by setting the heating temperature to T (° C.),
Using the heating time, using t (hr) and constant C,
It is expressed as (273 + T) × (C + logt). C is a constant, and a value of 17 to 23 is generally used in relation to the creep strength characteristics and the behavior of the structural change. Here, C = 20 which is a value with little data variation was experimentally used. The value of C is experimentally selected depending on the alloy to be applied.

[0011]

EXAMPLE A Co-based heat-resistant alloy ECY768 was used in air at 7
High-temperature and long-time heating was performed in the range of 50 ° C. to 1000 ° C. for a maximum of 5000 hours, and secondary carbides were observed for each heating material by a scanning electron microscope (hereinafter, referred to as SEM). As a typical example showing the structural change, FIG. 2 is a schematic view of an SEM image of a secondary carbide of an unheated ECY768 material, and FIG. Is shown.

The white particles in the figure are M ₂₃ C ₆ type secondary carbides 4, which can be seen to be coarsened by heating at a high temperature for a long time. FIGS. 4 and 5 show binarized images obtained by performing binarization processing in image analysis on FIGS. 2 and 3, respectively, and selecting seven images in descending order of particle size. The purpose of the binarization process is S
This is because the boundary between the secondary carbide and the matrix is unclear in the EM image, so that it is completely dichroic and the boundary is clear. The average area obtained by adding all the carbide areas in the binarized image and dividing the sum by the number is 0.03 in FIG.
7 [mu] m ^2, the FIG. 5 was 0.484μm ^2.

[0013] Graph showing a correlation between average area and LMP value of M ₂₃ C ₆ type secondary carbides ECY768 by various heating conditions thus obtained is shown in FIG 6. The white squares in the figure indicate that the heating temperature is 750 ° C., the black squares are 800 ° C., the white circles are 850 ° C., the black circles are 900 ° C., the white triangles are 950 ° C., and the black triangles are 1000 ° C. Here, as described above, assuming that the heating temperature is T (° C.) and the heating time is t (hr), the LMP value = (273+
T) × (C + logt). C is a constant, and 20 is used here.

Using FIG. 6, an LMP value corresponding to the average area of the M ₂₃ C ₆ type secondary carbide of the ECY768 material used for a long time in the actual machine was read. Next, the working temperature (metal temperature) is obtained by substituting the known actual machine operation time (hr) into the above LMP calculation formula.

The operation of the present invention will be described below. The Co-based heat-resistant alloy ECY768 is heated in the air at a temperature of 750 ° C. to 1000 ° C. for up to 5000 hours at a high temperature for a long time, and secondary carbides are observed by SEM for each heating material, and the change in average area is image-processed. Quantify using instrument. The average area of the secondary carbide shows a good correlation with the LMP value that is a function of temperature and time, and the metal temperature can be estimated from a temperature estimation diagram created by organizing them.

[0016] Therefore, compared with the conventional method of comparison with a limited photograph of a structure given as an experimental point of the heating temperature and time, the method of the present invention adopts the LMP value, so that the estimated temperature range is narrow. And the accuracy is improved.

[0017]

According to the present invention, the working temperature of a Co-based heat-resistant alloy can be objectively, quantitatively and accurately estimated.

[Brief description of the drawings]

FIG. 1: ECY768 subject to practice of the method of the present invention
5 is a photomicrograph of 500 times magnification showing the metallographic structure.

FIG. 2 is an SEM schematic diagram of an unheated secondary carbide of ECY768.

FIG. 3: ECY76 after heating at 1000 ° C. for 5000 hours
It is a SEM schematic diagram of the secondary carbide of No. 8.

FIG. 4 is a schematic diagram showing the binarized image of FIG. 2;

FIG. 5 is a schematic diagram showing the binarized image of FIG. 3;

FIG. 6 is a correlation curve between an average area of an M ₂₃ C ₆ type secondary carbide and an LMP value obtained by heating ECY768 at a high temperature for a long time.

[Explanation of symbols]

1 MC-type primary carbides 2 M ₂₃ C ₆ type primary carbides 3 dendrite boundary portion M ₂₃ C ₆ type secondary carbides 4 dendrite central portion M ₂₃ C ₆ type secondary carbides

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Keiichi Moriya 2-1-1, Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. No. 1 Inside the Mitsubishi Heavy Industries, Ltd. Takasago Factory

Claims (2)

[Claims] 1. A method for estimating the use temperature of a Co-based heat-resistant alloy, comprising the steps of: estimating a structural change associated with aging treatment of the Co-based heat-resistant alloy on the basis of a correlation curve associated with a Larson-Miller parameter which is a numerical value quantitatively representing the structure change; A method for estimating the use temperature of a Co-based heat-resistant alloy. 2. The method according to claim 1, wherein the Co-based heat-resistant alloy is an ECY768 material.